1. Field of the Invention
The present invention relates to MALDI sample plates.
2. Description of the Related Art
Matrix Assisted Laser Desorption Ionisation (“MALDI”) ion sources are typically used in conjunction with Time of Flight (“TOF”) mass spectrometers to analyse macro molecular samples such as peptides, proteins, polymers, DNA, RNA, intact bacteria or cells, carbohydrates, sugars etc.
In MALDI mass spectrometry, analyte is mixed with a matrix solution in an appropriate solvent and deposited on a MALDI sample plate for subsequent drying and crystallization. During the course of the drying process, crystal growth of the matrix is induced and analyte molecules become co-crystallised with the matrix. The MALDI sample plate is then inserted into a mass spectrometer and a relatively small (e.g. 100 μm diameter) laser beam is directed on to the sample plate. Photon bombardment causes the matrix and the analyte to be desorbed and ionised without substantially fragmenting the analyte. The desorbed ions are then mass analysed in the mass spectrometer. The matrix is an energy absorbing substance which absorbs energy from the laser beam thereby enabling desorption of analyte from the sample plate.
A MALDI sample plate is known which comprises a stainless steel plate coated with a 30-40 μm thick layer of hydrophobic polytetrafluoroethylene (also known as “PTFE” or Teflon (RTM)). 200 μm diameter hydrophilic gold spots are sputtered on to the hydrophobic surface using a photolithographic mask. The spots are spaced at 2.25 mm intervals so as to correspond with microtitre specifications. Small 1 μl sample droplets are then deposited on to the hydrophilic gold spots. After the solvent in the sample droplet has evaporated, the sample is deposited solely upon the 200 μm gold spots due to the strongly water repellent nature of the surrounding PTFE surface.